Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.33	11.210%	$89.335	$89.34	$89.35	$89.30
Purchase #2	$115.37	3.166%	$119.0226	$119.02	$119.00	$119.00
Purchase #3	$41.47	9.360%	$45.3516	$45.35	$45.35	$45.40
Purchase #4	$42.82	11.839%	$47.8895	$47.89	$47.90	$47.90
Purchase #5	$27.70	12.408%	$31.137	$31.14	$31.15	$31.10
Purchase #6	$95.29	4.207%	$99.2989	$99.30	$99.30	$99.30
Purchase #7	$138.95	12.246%	$155.9658	$155.97	$155.95	$156.00
7 purchase totals =	$541.93		$588.0004	$588.01	$588.00	$588.00